PEE-CAMBRIAN OF SCOTLAND , 23 



the region, and with 6-inches-to-the-mile ordnance maps of the highest 

 quality, to separate the Fundamental Complex into formations, except for 

 small areas. Probabl}' nowhere else in the world are the opportunities 

 better to make such separation if this were possible, and certainly no other 

 geological siirvey has spent more than a small fraction of the time given 

 by the Scotland survey to a small area of the Fundamental Complex. 



The petrographic descriptions show that the Lewisian is dominantly 

 composed of igneous rocks, of which the granitic type is most abundant, 

 and that the sediments are extremely subordinate. The latter rocks in- 

 clude "mica-schists, graphitic schists, quartz-schists, siliceous granulites, 

 limestones, dolomites, and cipolins."^^ 



The relations of the sediments of the Lewisian to the igneous series 

 have not been entirely worked out. Home says :" 



"There is no clear evidence that these types are intrusive in the former, but 

 in certain places the two are so intimately associated as to suggest that the 

 rocks of igneous origin may have been injected into those of sedimentary 

 origin. On the other hand, there is undoubted proof that, north of lalie Maree, 

 the altered sediments rest on a platform of gneiss and are locally overlain by 

 gneiss with basic dikes, the superposition of the gneiss on the sediments being 

 there due to folding and thrusting." 



In the strongest possil)le contrast with the Lewisian is the Torrid- 

 onian. Here ordinary stratigraphic methods apply and the system has 

 been divided into three divisions or formations. It is clear that under 

 the general classification advocated in this paper the Torridonian is 

 Algonkian and the Lewisian Archean. 



While the foldings, faultings, intrusions, and metamorphisms of the 

 Archean have been 1 so extreme and the relations of the different rocks so 

 intricate that upon. the general geological maps there has been no attempt 

 to subdivide the Fundamental Complex, the descriptions show that in the 

 central district basic rocks are developed in great force with subordinate 

 amounts of ultra basic rocks, and that in the northern and southern dis- 

 tricts the acid rocks are dominant. Moreover, it is stated that the basic 

 rocks are the oldest group and are intruded by the acidic gneisses. Thus 

 we api)arently have in the Archean complex the equivalent of the Kee- 

 watin and Laurentian, as we use these terms in America, with like 

 relations. Finland 



In Finland for many years Sederholm has been at work on the pre- 

 Cambrian rocks. His studies there result in a classification which is 

 closely analogous to that of tlie Lake Superior region. His succession is 

 as follows : 



Memoirs of the Geological Survey of Great Britain. The geological structure of 

 the northwest Highlands of Scotland, 1907, p. 75 

 " Ibid., p. 4. 



